A leadframe forms the base or skeleton of an IC package, providing mechanical support to semiconductor dies during assembly into a finished package. A leadframe typically includes a die paddle for attaching a semiconductor die, and leads providing the means for external electrical connection to the die. The die can be connected to the leads by wires, e.g. through wire bonding or tape automated bonds. Leadframes are typically constructed from flat sheet metal, e.g. by stamping or etching. The sheet metal is typically exposed to chemical etchants that remove areas not covered by photoresist. After the etching process, the etched frames are singulated (separated) into leadframe strips. Each leadframe strip includes a number of unit leadframes each having the die paddle and lead construction described above.
Semiconductor dies attached to the die paddles after completion of the assembly process of a leadframe strip are typically tested after separation of the unit leadframes from the leadframe strip, e.g. by punching. Alternatively, the unit leadframes remain mechanically connected to the leadframe strip by tie bars during die testing. This is commonly referred to as leadframe strip testing. Separation of the individual unit leadframes from the leadframe strip occurs after electrical testing. However, the devices must be electrically isolated from one another prior to leadframe strip testing to ensure proper device testing.
The electrical isolation process conventionally involves severing the die paddle and lead connections along a final lead outline of the unit leadframes. The final lead outline corresponds to the regions of the leadframe strip to be severed after strip testing e.g. after molding in order to separate or singulate the unit leadframes into individual packages. Severing the leads along the final lead outline of the unit leadframes limits the amount of contact area available for probing the leads, which is particularly problematic for leadless and short lead packages that have very small lead contact area inside the final lead outline for probing. Many of these packages are rated for high current operation, but conventional leadframe strip testing often cannot be performed at such high current limits due to the small contact area available for probing the leads. For example, a package rated at 40 A may only be tested at 30 A or a package rated at 100 A may only be tested at 50 A at most using conventional leadframe strip testing approaches.